There have been heretofore many nitride semiconductor light emitting elements, such as LEDs (light emitting diodes) and semiconductor lasers, in which a light emitting element structure including a plurality of nitride semiconductor layers is formed on a substrate of sapphire or the like by epitaxial growth. The nitride semiconductor layer is represented by the general formula: Al1-x-yGaxInyN (0≤x≤1, 0≤y≤1, 0≤x+y≤1).
The light emitting structure has a double-hetero structure in which an active layer including a nitride semiconductor layer of single-quantum-well structure (SQW) or multi-quantum-well structure (MQW) is sandwiched between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer. When the active layer is an AlGaN-based semiconductor layer, by adjusting an AlN molar fraction (also referred to as an Al composition ratio), band gap energy can be adjusted within a range where band gap energies that can be taken by GaN and AlN (about 3.4 eV and about 6.2 eV) are lower and upper limits, so that an ultraviolet light emitting element having a light emission wavelength of about 200 nm to about 365 nm is obtained. Specifically, when a forward-current is caused to pass from the p-type nitride semiconductor layer to the n-type nitride semiconductor layer, light emission matching the band gap occurs in the active layer.
The nitride semiconductor ultraviolet light emitting element is put to practical use after being sealed with an ultraviolet-transparent resin such as a fluorine-based resin or a silicone resin as disclosed in FIGS. 4, 6 and 7 etc. in Patent Document 1 or FIGS. 2, 4 and 6 etc. in Patent Document 2. The sealing resin protects an inside ultraviolet light emitting element from an outside atmosphere to prevent degradation of the light emitting element due to ingress of moisture, oxidation and the like. Further, the sealing resin may be provided as a refractive index difference mitigation material for improving light extraction efficiency by mitigating a reflection loss of light resulting from a refractive index difference between a light condensing lens and an ultraviolet light emitting element or a refractive index difference between a space to be irradiated with ultraviolet light and an ultraviolet light emitting element. Further, irradiation efficient can be improved by shaping the surface of the sealing resin into a light condensing curved surface such as a spherical surface.